This invention relates to tabletting machines and concerns tabletting machines of the kind (hereinafter referred to as of the kind described) in which the powdered or granulated material to be tabletted is fed onto the surface of a rotating die table so as to fill dies in the die table and be compressed into a tablet in each die between a pair of punches, one of the punches being subsequently withdrawn from the die and the other punch being pushed through the die to eject the tablet from the die.
In a conventional tabletting machine of the kind described, the die table is horizontally disposed and individual pairs of punches operate vertically to enter the dies from opposite ends, the punches being operated by stationary cams. Means is provided for adjusting the cams thereby to adjust the amount of material which is compressed in each die to form each tablet and the thickness of the resulting tablet.
In our British Patent Nos. 1,481,797 and 1,481,798 we describe a tabletting machine of the kind described having a continuous, adjustable cam track to operate radially outer punches, there being radially inner and outer punches operating radially with respect to the axis of rotation of a concave cylindrically surfaced die table. The use of a continuous, adjustable cam track avoids noise and wear problems encountered in conventional tabletting machines. The use of a cylindrical die table having a concave cylindrical surface has the advantage that powdered or granulated material to be tabletted moves from the surface of the die table into the dies with the assistance of centrifugal force so that feeding of the material to be tabletted, into the dies, is improved.
A problem which arises with tabletting machines in general is that relatively movable bearing surfaces of the machine are liable to contamination and wear by the material being tabletted. This is particularly true of the sliding bearing surfaces of the punches and the punch guides which require to be positioned adjacent the die table.
An object of the present invention is to reduce or eliminate this problem more particularly, although not exclusively, in a tabletting machine in which the punches operate radially of the axis of rotation of the die table.
In such a machine, the space available to the radially inner punches is restricted.